The role of echocardiography in the assessment of cardiac function in weightlessness-Our experience during parabolic flights.

Parabolic flight (PF) elicits changes in hydrostatic pressure gradients, resulting in increase (at 0Gz) or decrease (at 1.8Gz) in cardiac preload. The magnitude of these changes on left ventricular (LV) and atrial (LA) volumes, as well as on myocardial velocities, strain and strain rates, is largely unknown. Using real-time 3D (RT3DE) and Doppler tissue echocardiographic imaging (DTI) during PF in normal subjects in standing position, we showed that both LV and LA volumes were decreased at 1.8Gz and increased at 0Gz by about 20% and 40%, respectively. Previous 2D or M-mode studies underestimated such changes. Also, preload dependence was confirmed for systolic and diastolic velocities, and peak systolic strain, while strain rates were preload independent, probably reflecting intrinsic myocardial properties. Low body negative pressure at -50mmHg applied during 0Gz was effective in restoring 1Gz levels. RT3DE and DTI during PF are feasible, allowing the evaluation of the cardiac function under different loading conditions.